Apparatus for pattern controlled electrode movement for E.D.M.

ABSTRACT

In an electro-discharge machining apparatus for progressively conducting precise machining through relative approach movements between an electro-discharge machining electrode and a workpiece in the horizontal direction substantially perpendicular to a direction in which the electrode is opposed to the workpiece, a pattern generator generates basic movement patterns for relative approach movements, a pattern designator designates desired patterns in basic movement patterns to respective sections obtained by dividing a movement region of respective approach movements within the horizontal plane, step amount designators designate the step amounts for actual relavtive approach movements in the respective sections, and actual trajectories are computed for actual relative approach movements based on data designated by the pattern designator and step amount designator.

This application is a division of application Ser. No. 178,235, filedAug. 14, 1980, now U.S. Pat. No. 4,367,391.

This invention relates to an electro-discharge machining method andapparatus, and more particularly to an electro-discharge machiningmethod and apparatus which is capable of achieving preciseelectro-discharge machining.

In general, to machine a workpiece of a metal etc. by electro-dischargemachining, using an electro-discharge machining electrode, the electrodeis first shaped to have a size and a contour coinciding with a desiredsize and contour to be formed on the workpiece through the machining andpositioned in an opposite relation to the workpiece, and then theelectrode and the workpiece are subjected to relative approachingmovement in the vertical direction to machine the workpiece forproviding the desired size and contour by electro-discharging. However,such electro-discharge machining by simple relative movement in thevertical direction between the electrode and the workpiece cannotprovide satisfactory precision in size and surface of the obtainedproduct. By this reason, in a recently proposed electro-dischargemachining method and apparatus, not only a relative machining operationin the vertical direction between the electrode and the workpiece iscarried out to achieve rough machining or semi-finish machining but arelative approach operation in the horizontal direction between theelectrode and the workpiece is repeated to an extent corresponding to amargin to be trimmed to achieve finish machining on the workpiece forobtaining precise dimensions and a surface of the machined workpiece (asdisclosed, for example, in U.S. Pat. No. 4,168,426). However, therelative approach movement in the horizontal direction as proposed inthis known method and apparatus only provides a fixed pattern ofmovement uniformly to the face of the workpiece according to theconfiguration of the electrode or the required configuration of theworkpiece. Therefore, it is impossible to apply a precisefinish-machining operation to a narrow corner portion of the workpieceor to locally apply an accurate finish-machining operation to acomplicated portion of the workpiece. Thus, the conventional method andapparatus cannot provide a satisfactory result except for a portionhaving a relatively simple configuration. In addition, due to difficultyof precise local finish operation, the operating efficiency of theelectro-discharge machining is not satisfactory, either.

It is therefore an object of the present invention to provide anelectro-discharge machining method and apparatus which are capable ofobviating the disadvantages involved in the known electro-dischargemachining method and apparatus.

It is another object of the present invention to provide anelectro-discharge machining method and apparatus which are capable oflocally applying precise finish-machining onto a complicated surface ofa workpiece.

It is still another object of the present invention to provide anelectro-discharge machining method and apparatus which are capable ofautomatically achieving precise finish-maching in an electro-dischargemachining.

In accordance with the present invention, there is provided anelectro-discharge machining method for progressively carrying outprecise machining through relative approach movements between anelectro-discharge machining electrode and a workpiece in the horizontaldirection substantially perpendicular to a direction in which saidelectrode is relatively opposed to said workpiece, which method ischaracterized by dividing a movement area of said relative approachmovements into a plurality of quadrants within the horizontal plane andselecting trajectories of said relative approach movements for therespective quadrants for successively and progressively achieving themachining.

Further in accordance with the present invention, there is provided anelectro-discharge machining apparatus for progressively conductingprecise machining through relative approach movements between anelectro-discharge machining electrode and a workpiece in the horizontaldirection substantially perpendicular to a direction of verticalmachining operation in which said electrode and said workpiece areopposed to each other, which apparatus comprises pattern generatingmeans for generating basic operation patterns for respective quadrants;pattern designating means for designating patterns of said relativeapproach movements to the respective quadrants within the horizontalplane; step amount designating means for designating step amounts ofactual relative approach movements depending upon trajectories in therespective quadrants, the trajectories being proportioned to thedesignated patterns; computing and storing means for computing andstoring trajectories for the actual relative approach movements based onpattern data designated by said pattern designating means and data fromsaid step amount designating means; output control means forsequentially outputting data stored in said computing and storing means;and operating means for carrying out required relative approachmovements according to data outputted from said computing and storingmeans.

Further objects and advantages of the invention will be apparent fromthe following description taken in connection with the accompanyingdrawings.

FIG. 1 is a diagrammatic perspective view of part of a machining portionin a general electro-discharge machining appartus;

FIG. 2 is a sectional view of the machining portion illustrated in FIG.1 which is taken along a line II--II in FIG. 1 for explaining theelectro-discharge machining method and the quadrants in accordance withthe present invention; and

FIGS. 3A and 3B are block diagrams of one form of a control section inan electro-discharge machining apparatus embodying the presentinvention.

FIG. 1 shows a diagrammatic perspective view of an electro-dischargemachining apparatus for explaining a common electro-discharge machiningmethod and apparatus which carry out relative approach movements in thehorizontal direction. An electro-discharge machining electrode 14 isprovided with a stem 12 and formed to have a desired configuration andsize. The electrode 14 is held by and connected to a spindle 10 of theelectro-discharge machining apparatus so as to be movable in Z-axisdirection (vertical direction). A pulse voltage for electro-dischargemachining is applied by a pulse voltage source (not shown) across a gapbetween the electrode 14 and a workpiece 18 placed on a table 16 of theelectro-discharge machining apparatus in an opposite relation to theelectrode 14. A nut 70 fixed to the spindle 10 is in mesh with one endof a threaded rod 72. The other end of the threaded rod 72 is coupled toa driving shaft of a pulse motor 74, so that the electrode 14 is movedin the Z-axis direction according to the rotation of the pulse motor 74.When the pulse motor 74 is driven and the electrode 14 is moveddownwardly, electro-discharge occurs between the electrode 14 and theworkpiece 18 to form a hollow portion 18a on the workpiece 18 in aconfiguration corresponding to the configuration of the electrode 14.

As mentioned above, to form the hollow portion 18a by rough-machining,the electrode 14 is successively fed downwardly in the Z-axis direction,causing progressive electro-discharge machining. On the other hand, in astep of rough-machining of the hollow portion 18a, to provide a precisemachined face on the hollow portion 18a the table 16 is fed inch by inchin X-axis and/or Y-axis direction within the horizontal plane. Thus, theworkpiece 18 is allowed to make approach movements relative to theelectrode 14 in the horizontal direction to apply finishelectro-discharge machining to the roughly machined bored portion 18a.To displace the table 16 in the X-axis direction, a threaded rod 78meshed with a nut 76, which is fixed to the table 16, is rotated by apulse motor 80 imparting X-axis direction movement to the table 16. Onthe other hand, to displace the table 16 in the Y-axis direction, amovable base 82, on which whole of the table 16 is placed, is moved by adrive mechanism comprised of a nut 84 fixed to the movable base 82, athreaded rod 86 in mesh with the nut 84 and a pulse motor for rotatingthe threaded rod 86, conjointly moving the table 16 in the Y-axisdirection. This drive mechanism for moving the table 16 on which theworkpiece is mounted is common to an ordinary electro-dischargemachining apparatus and therefore a further detailed description thereofis omitted. However, in this connection, it is to be noted thataccording to the conventional electro-discharge machining method, thetable 16 is moved only uniformly in the X-axis and Y-axis directionswithin the horizontal plane. It cannot always assure precise finishbecause a precise finished surface cannot be obtained when the hollowportion 18a has a complicated configuration. Therefore, the presentinvention contemplates an electro-discharge machining method andapparatus which is capable of applying precise local finish-machiningnot only to the portion 18a having a female configuration as illustratedin FIG. 1 but to a machined portion having a male configuration andfurther capable of enhancing the operating efficiency ofelectro-discharge machining. More specifically, in the presentinvention, for applying relative approach movements in the X- and Y-axisdirections within the horizontal plane between the electrode 14 and theworkpiece 18, the movement area is divided into a plurality of quadrantswithin the horizontal plane and machining is progressively carried outby designating trajectories of the relative approach movements for therespective quadrants.

The quadrants of the movement area within the horizontal plane will nowbe explained.

FIG. 2 illustrates sections of the electrode 14 and the workpiece 18taken by the horizontal plane for the convenience of explanation. InFIG. 2, to impart approach movements to the workpiece 18 relative to theelectrode 14, the movement area is divided, for example, into fourquadrants, i.e., first, second, third and fourth quadrants with a pointP as a center. The number of the quadrants may be increased or reduced,but not to one, according to necessity. Thus, a plurality of quadrantsare provided and trajectories of the relative approach movements areselected for the quadrants, respectively. For instance, in FIG. 2, eachof the first and the second quadrant is assigned with an arcuatetrajectory and each of the third and the fourth quadrant is assignedwith a rectangular trajectory. In this connection, it is to be notedthat the conventional relative approach movements in the horizontalplane according to the known electro-discharge machining method cannever have two kinds of trajectories such as an arcuate trajectory and arectangular trajectory as provided in the present invention. Therefore,according to the known electrode-discharge machining method, if finishmachining is conducted with a view to improvement of an arcuate face ofthe hollow portion 18a, finish machining for a corner of the portion 18ais not satisfactory, while if finish machining is conducted mainly forimprovement of the corner of the portion 18a, the arcuate face thereofcannot have a sufficient result.

The formation, operation and effect of the electro-discharge machiningapparatus for carrying out the electro-discharge machining method of theinvention will now be described referring to FIG. 3.

FIG. 3 is a block diagram of one form of a control section of theelectro-discharge machining apparatus for progressively achievingelectro-discharge machining according to the desired trajectoriesselected for the respective quadrants. In FIG. 3, switch mans 30 setsand inputs, in the form of digital data, amounts of steps which tracethe trajectory selected for each of the quadrants. The step amount of,for example, from 3 μm to 9.999 mm can be set by an operator whooperates four-digit digital switches 20a to 20d. The step data set bythe swtich means 20 is stored in a step data latch memory 22.

On the other hand, a pattern selecting switch device 24 comprised atfour switches 24a to 24d is provided to designate trajectory patterns ofthe relative movements which is to be implemented in the respectivequadrants. The switches 24a to 24d of the pattern selecting switchdevice 24 output selecting data D₁, D₂, D₃ and D₄ corresponding torespective patterns P₁ to P₄ selected for the areas of the first tofourth quadrants, respectively. These selecting data D₁ to D₄ areinputted to pattern generators 26, 28, 30 and 32, respectively. Each ofthe pattern generators 26, 28, 30 and 32 stores therein a plurality kindof preset basic patterns. A basic pattern selected by a correspondingswitch is selected according to the selecting data, and a desiredselected pattern data is swept out in response to a clock pulse producedby a clock pulse generator 34. The sweeping-out operations of patternsfrom the respective pattern generators 26, 28, 30 and 32 are carried outin the order pursuant to a sweeping-out command signal CS.sub. 1 from aprogram counter 36.

The pattern generator 26 has four output lines +X₁, -X₁, +Y₁ and -Y₁ andprovides a trajectory information by outputting a pulse to an outputline corresponding to an information for moving the workpiece 18 in apositive X-axis direction, in a negative X-axis direction, in a positiveY-axis direction or in a negative Y-axis direction within the X-Ycoordinate plane. Each of the other pattern generators 28, 30 and 32 hassimilarly four output lines, and the output lines of these patterngenerators are denoted by similar marks having different suffixes inFIG. 3. A group of the output lines designating the same coordinatedirection are coupled commonly to each other and coupled to an inputterminal of a rate multiplier 38, 40, 42 or 44. Each of the ratemultipliers 38, 40, 42 and 44 receives a latch data D₅ latched in thestep data latch memory 22 so that input signals to the respective ratemultipliers are demultiplied according to contents of the latch data D₅.As a result, output data D₆ to D₉ from the respective rate multipliers38 to 44 are obtained as desired actual movement trajectory data overthe four quadrants according to the basic patterns selected by thepattern selecting switch means 24 and the step amounts selected by theswitch device 20. The data D₆ designates information of a positiveX-axis direction movement, D₇ information of a negative X-axis directionmovement, D₈ information of a positive Y-axis direction movement and D₉information of a negative Y-axis direction movement. Actual movementtrajectory data D_(a) comprised of the data D₆ to D₉ is stored in amemory 46. Operations of writing into and reading out of the memroy 46are controlled by a command signal CS₂ from the program counter 36.

Prior to carrying out the relative approach movements between theelectrode 14 and the workpiece 18 in the horizontal direction to tracethe selected movement trajectories and carrying out preciseelectro-discharge machining, a start pattern generator 48 produces astart pattern for moving, relative to the electrode 14, the workpiece 18to a starting coordinate point of the movement trajectories. The startpattern generator 48 is connected to a start button 50. Upon depresionof the start button 50, the level of a line 52 becomes "1" to establisha condition where the start pattern corresponding to the contents of thelatch data D₅ is read out. The reading-out operation of the startpattern is implemented by a reading-out clock RC₁ from the programcounter 36. The read-out data are fed to a bus line 54 for X-axis and toa bush line 56 for Y-axis data and applied to the X- and Y-axisdirection drive mechanism of the electro-discharge machining apparatusas described above. Therefore, the drive mechanism displaces, forexample, the table 16 as illustrated in FIG. 1 in the X-axis directionand/or in the Y-axis direction to allow relative approach movementbetween the electrode 14 and the workpiece 18, according to the startpattern, into the starting coordinate point of the movement trajectoriescorresponding to the selected patterns. When an ejection detectingcircuit 58 detects completion of ejection of the start pattern from thestart pattern generating circuit 48, a detection signal S₁ is inputtedto the program counter 36. when the program counter 36 receives thesignal S₁, it detects a state ready to initiate preciseelectro-discharge machining by tracing the relative approach movementtrajectories accoding to the patterns selected for the respectivequadrants and outputs a command signal CS₂ so as to supply the actualmovement trajectories data stored in the memory 46 to the bus lines 54and 56. The data for actual movement trajectories supplies to the buslines 54 and 56 are applied to the X- and Y-axis drive mechanism so thatthe table 16 (FIG. 1) is displaced in X-axis and/or Y-axis direction tofollow, in the respective quadrants, the trajectories of the relativeapproach movements according to the selected patterns for achieving adesired precise electro-discharge machining. When the trajectory in thefinal quadrant, for example in the fourth quadrant as in the illustratedembodiment, has been passed, a reading-out clock RC₂ is applied from theprogram counter 36 to an end pattern generating circuit 60 and an endpattern is generated from the end pattern generating circuit 60 toreturn the relative position between the electrode 14 and the workpiece18 to the origin point P (FIG. 2). The step amount of the end patterngenerated from the end pattern generating circuit 60 depends upon thestep amount data stored in the step data latch memory 22. The endpattern generated from the end pattern generating circuit 60 is suppliedto the bus lines 54 and 56 and applied to the X- and Y-axis directiondrive mechanism to displace the table 16 (FIG. 1) in the X-axis and/orY-axis directions to the origin point P in the same manner as in case ofthe start pattern. Thus, one cycle of the electro-discharge machining iscompleted, but the following cycle of the electro-discharge machiningmay further be conducted through assistance of the program counter 36.To fully stop the operation of the electro-discharge machiningapparatus, a stop command button 59 may be depressed to feed a stopcommand signal to the program counter 36, which will stop the outputtingof the data of the actual movement trajectories from the memory 46. Ofcourse, the stop command button 59 may be operated in any cycle of theelectro-discharge machining operation to cause the program counter 46 togenerate stop command signal. The program counter 36 may be coupled to avoltage controlled oscillator 62 which is responsive to a voltage Vgacross a gap between the electrode 14 and the workpiece 18 for producinga pulse signal S₃ having a frequency corresponding to the gap voltageVg, so that the program counter 36 may be servo-controlled to commandthe memory 46 to feed data at a speed corresponding to the frequency ofthe pulse signal S₃. With this formation, the electro-dischargemachining operation following the trajectories of the relative approachmovements in the respective quadrants can be controlled with respect toits operation speed. Therefore, if chips exist in the gap between theelectrode 14, and the workpiece 18, the speed of the electro-dischargemachining operation may be increased to expel the chips out of the gap.Furthermore, electric discharge interruption detecting signal S₂ may beinputted to the program counter 36 to provide, to the counter 36,information of electric discharge interruption during theelectro-discharge machining operation according to the selectedpatterns. In this case, if electric discharge across the gap between theelectrode 14 and the workpiece 18 is interrupted, electro-dischargemachining operation progressing along the trajectories of the relativeapproach movements in the respective quadrants can be suspended to avoidan idle operation of the electro-discharge machining apparatus.

In the arrangement as illustrated in FIG. 3, each of the patterngenerating circuits or the pattern generators may be formed of a knownROM (read-only memory) and the latch memory may be formed of a RAM(random access memory). This formation allows employment of a commercialmicrocomputer available at a reasonable price in the market forconstructing the arrangement of FIG. 3 and therefore enables reductionin manufacturing cost of the entire electro-discharge machiningapparatus.

What is claimed is:
 1. An electro-discharge machining apparatus forprogressively conducting precise machining through relative straight andarcuate approach movements between an electro-discharge machiningelectrode and a workpiece in the horizontal direction substantiallyperpendicular to a direction in which said electrode is opposed to saidworkpiece, which apparatus is characterized by divider means dividing amovement region of said relative approach movement into a plurality ofstraight and arcuate sections with in the horizontal plane anddesignating trajectories of sid relative straight and arcuate approachmovements for the respective straight and arcuate sections forsuccessively and progressively achieving the machining.
 2. Anelectro-discharge machining apparatus for progressively conductingmachining through relative approach movements between anelectro-discharge machining electrode and a workpiece in the horizontaldirection substantially perpendicular to a direction in which saidelectrode is opposed to said workpiece, which apparatus is characterizedby pattern generating means for generating basic movement patterns forsaid relative approach movements; pattern designating means fordesignating desired patterns in said basic movement patterns to therespective section which are obtained by dividing a movement region ofsaid relative approach moements within the horizontal plane; step amountdesignating means for designating the step amounts for actual relativeapproach movements in the respective sections; computing and storingmeans for computing actual movement (trajectories) trajectory data fortracing said actual relative approach movements based on basic patternselection data designated by said pattern designating means and stepamount data and storing therein data of said actual trajectories; and,actuating means for carrying out relative approach movements inaccordance with contents stored in said computing and storing means,wherein said actuating means comprises a voltage-controlled pulsegenerator for outputting a pulse signal having a frequency correspondingto a voltage across a machining gap, and a reading-out speed of datastored in said computing and storing means is controlled according tosaid voltage across said machining gap, the computing and storing meanscomprising means for converting said basic movement patterns outputtedfrom said pattern generating means into actual movement patterns basedon the data from said step amount designating means and means forstoring data outputted from said converting means, the approachmovements comprising straight and arcuate approach movements and saidpattern generating means comprising means for generating basic straightand arcuate patterns.
 3. An electro-discharge machining apparatus forprogressively conducting precise machining through relative straight andarcuate approach movements between an electro-discharge machiningelectrode and a workpiece in the horizontal direction substantiallyperpendicular to a direction in which said electrode is opposed to saidworkpiece, which apparatus is characterized by generator meansgenerating basic straight and arcuate movement patterns for saidrelative approach movements, divider means dividing a movement region ofsaid relative approach movements within the horizontal plane intorespective straight and arcuate sections, designator means designatingdesired straight and arcuate patterns in said basic movement patterns tothe respective sections, designator means designating step amounts ofactual relative approach movements in the respective sections, computingmeans for computing actual trajectories for said actual relativestraight and arcuate approach movements based on designated patterns,and means for storing data of actual trajectories and means to carry outrelative straight and arcuate approach movements in accordance withstored data.